Device for reducing energy losses in a machinery unit

ABSTRACT

The present invention relates to a device for reducing energy losses in a machinery unit ( 1 ), having at least one part ( 4 ) which is arranged to rotate in fluid about a rotation axis ( 6 ) in a substantially closed chamber ( 3 ) delimited in the radially outward direction by means of a wall ( 18 ) extending around the rotation axis. The wall ( 18 ) has a radially inward facing wall surface ( 10 ) extending wholly or partially around the revolution, which wall surface is highly smooth and extends close to, but with an interspace ( 14 ) to the radially outer surface which is generated around the revolution by the rotary part ( 4 ). The interspace is suited to minimizing the rotating fluid volume and, at the same time, maintaining necessary width for a boundary layer in the fluid between the generated surface and the wall surface.

BACKGROUND OF THE INVENTION Technicl Field

The present invention relates to a device for reducing energy lossesaccording to the preamble to subsequent patent claim 1.

In machinery units which have parts rotating in a fluid, for exampleoil, energy losses arise due to the braking effect of the fluid as aresult of the fluid being jointly transported in the rotation of theparts and braked by friction against rough or otherwise uneven surfacesin the chamber enclosing the fluid and the rotating parts. Examples ofsuch machinery units are gearboxes, internal combustion engines,hydraulic motors and pumps.

In certain types of machinery units, further energy losses accrue due tothe fluid being rotated in a chamber which is asymmetrical around arotating part, such as in displacement-type hydraulic motors and pumpshaving a so-called driving pulley, which is angled relative to axialpistons in a cylinder drum and converts axial forces into torque andvice versa, see, for example, SE 7208028-6. As a result of thispublication, it is previously known to reduce energy losses by the useof a partitioning member in the form of a radially directed,circumferential projection on the inside of the machine housing.However, the loss reduction is relatively limited due to the fact thatthe separated fluid continues to rotate with the rotating component andis also compressed as it rotates around, one revolution with therotating component.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is to increase efficiency byreducing the energy losses in a machinery unit having rotating parts influid by virtue of the fact that, on the one hand, only a limited partof the total fluid volume is jointly transported in the rotation,whilst, at the same time, the jointly rotating volume is carried alongwith low friction.

Another object of the present invention is achieved by means of adevice, including one part which is arranged to rotate in fluid about arotation axis in a substantially closed chamber delimited in theradially outward direction by means of a wall extending around therotation axis, wherein in the wall has a radially inward facing wallsurface extending wholly or partially around the revolution, the wallsurface is a highly smooth low-friction surface against the fluid andextends close to, but with an interspace to the radially outer surface,which is generated around the revolution by the rotary part, and whereinthe interspace is suited to minimizing the rotating fluid volume and, atthe same time, maintaining necessary width for a boundary layer formedin the fluid between the generated surface and the wall surface.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in greater detail below with a pair ofillustrative embodiments with reference to appended drawings, in which

FIG. 1 shows diagrammatically a first embodiment of a device accordingto the invention, applied to a gearbox,

FIG. 2 shows a longitudinal section through a hydraulic pump/motorprovided with a device according to the invention in a secondembodiment,

FIG. 3 is a perspective view of the device according to the invention inthe second embodiment,

FIG. 4 is a side view of the device according to FIG. 3,

FIG. 5 is a section through the device along the line V-V in FIG. 4, and

FIG. 6 is a partially cut section of a variant of the hydraulicpump/motor according to FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings and initially FIG. 1, thus shows the device ina first embodiment in order to illustrate the principle of reducingenergy losses according to the invention. FIG. 1 shows a section througha machinery unit 1, which can be constituted by, for example, agear-tooth type gearbox having a gearbox housing 2 enclosing a chamber 3which is wholly or partially filled with a fluid, such as oil, whosetask is to reduce friction between metal parts and counteract wear andtear, and also, in many cases, to cool. Depending on a number offactors, such as the viscosity of the fluid and the character of thechamber, the fluid does, however, involve energy losses as a result ofthe fluid countering the torque which is applied to the rotating partsin the machinery unit. As shown in FIG. 1, these are constituted by gearwheels 4, 5, one of which is shown in its entirety. This is rotatablerelative to a rotation axis 6, either by the gear wheel being fittednon-rotatably to the shaft and driven around the second by the gearwheel 5, with which the gear wheel 4 is meshed. As a result,particularly, of deformation of the gear wheels in the course of therotation revolution, i.e. deviation from a smooth cylinder jacketsurface, the fluid, to a great extent, is rotated with the gear wheels.In the case of a conventional gearbox, the whole of the fluid volume isrotated and, at the same time, with its outer sections, is braked by theinner walls of the gearbox housing 2, which walls usually have a certaincoarseness due, for example, to the chosen production method, such ascasting. Apart from the surface structure of the inner wall of thehousing 2, a non-rotationally-symmetric volume of the chamber 3, in thiscase an angular or rectangular cross-sectional form, means that thejointly transported fluid is subjected to a local increase in pressurein the narrower portions, similar to a restriction in a pipe, therebyresulting in further energy losses.

According to the invention, a screening member 8 is therefore provided,in the form of a screen wall which, as shown in FIG. 1, extendspartially around at least one of the rotary parts, i.e., in FIG. 1, thegear wheel 4 and the rotation axis 6. The screen wall is substantiallyin the shape of a cylinder jacket and extends relatively close to thetooth tips 9 of the gear wheel, yet such that a radial interspace in theform of a gap is formed between the tooth tips and the radially inwardfacing surface 10 of the screen wall, which surface is highly smooth soas to create as little friction as possible against the enclosed fluid.The screen wall is closed off along two transverse edges 11, 12, which,in this case, are bent radially outward. In the illustrated example, thescreen wall is expediently unaltered in its section viewed transverselyto the plane of the paper, but can have edges which separate the teethalso in the axial direction so as further to reduce the losses. Thechamber 3 in the housing 2 is thereby divided into a, relative to therotation axis 6, radially outer part-chamber 13 and radially innerpart-chamber 14. Apart from by opposite end walls and top wall (notshown), the outer part-chamber 13 is limited by the wall sides 15, 16,17 of the housing and by the outside 18 of the screen wall 8, whichlatter, as shown in FIG. 1, is likewise in the shape of a cylinderjacket, since the screen wall is realized in a suitable uniformly thickyet relatively thin material, for example steel plating, which is bentinto the desired shape. The inner part-chamber 14 is likewise delimited,apart from by end walls (not shown), by the inside or inner surface 10of the screen wall, which produces low friction against the fluid, andby the surfaces of the rotary parts 4, 6 if the part-chamber is hereinregarded as the chamber which can be filled by the particular fluid,i.e. oil.

The arrangement in which the smooth wall surface 10 is situated at anoptimal distance from the rotating part 4 thus produces, as a result ofthe previously described division of the fluid chamber according to FIG.1, an outer part-chamber which has no rotating parts and an innerpart-chamber 14 which encloses rotating parts, thereby reducing energylosses incurred due to the action of the fluid. The fluid in the innerpart-chamber is jointly rotated, in fact, together with the rotatingparts with minimal friction and pressure-change losses, whilst, at thesame time, the fluid in the outer chamber is separated from the rotatingparts and is not forced to flow along the inner walls of the housing,but rather, in an extreme case, is kept almost stationary. The jointlyrotating fluid volume thus flows around along the smooth inside 10 ofthe screen wall 8, which smooth inside extends in a rotationallysymmetrical manner around the rotation axis 6 up to its end edges 11,12. A certain exchange and overflow occurs between the fluid volume inthe inner part-chamber 14 and the outer part-chamber 13 and is necessaryto maintaining the properties of the oil, i.e. too low a fluid volume,such as the volume in the inner chamber 14, produces an inadequateworking life for the oil, i.e. demands unfavorably short oil changeintervals, in addition to which energy losses in the exchange might needto be evacuated with the oil.

The second embodiment of the screening member according to the inventionwill now be described with reference to FIGS. 2-6. This secondembodiment is intended to reduce energy losses in a hydraulic pump ormotor, which, in FIG. 2, is of a type described in the applicant's ownpatent publication WO99/30034. This hydraulic machine is of thedisplacement type, more precisely of the “bent axis” type, in which thedrive shaft 20 of the machine has a rotation axis 21 which is angledtoward a second rotation axis 22, about which a cylinder drum 23 isintended to rotate together with a number of, for example five, axialpistons 24, which move to and fro, i.e. reciprocally, in theirrespective cylinder bores 25, which latter extend parallel with thesecond rotation axis 22 and are arranged in a circle viewed from theends of the cylinder drum 23. As a result of the odd number of cylinderbores and pistons as illustrated in FIG. 2, and the regular distributionthereof, the cylinder bores are not arranged opposite one another inpairs, so that only one cylinder bore is seen in FIG. 2. A hydraulicpump or motor having an even number of cylinder bores, such as six oreight, with cylinder bores arranged diametrically opposite one anotherin pairs, is shown, for the sake of clarity, in part-section in FIG. 6.With reference to both FIGS. 2 and 6, it can be seen that the axialpistons extend out through one end of their cylinder bores with a pistonrod 26, which at its outer end transcends into a spherical head 27,which is mounted in a corresponding cup-shaped bearing 28, one bearingcup for each piston, in a driving pulley 29, which pulley is fixedlyattached to the inner end of the drive shaft 20 and extendsperpendicularly to the rotational axis 21 of the latter. As a result ofthe driving pulley 29 forming an angle to the rotation axis 22 of thecylinder drum, a rotation motion of the drive shaft 20 is created by theaxial motions of the pistons, or vice versa, depending on whether themachine is constituted by a pump or a motor. Through alternate fillingand emptying of the cylinder bores with hydraulic fluid, pumping actionis created in a known manner in the hydraulic fluid in the case of apump and, conversely, a torque on the drive shaft 20 in the case of amotor. In the case of a pump, a drive motor is coupled to the driveshaft 20, which, thus, is an input shaft for driving of the pump, whilstin the case of a motor a hydraulic pressure in the pressure fluidcreates torque on the drive shaft 20, which here is an output shaft. Thedrive shaft 20 is vertical in FIG. 2, but can have any directionwhatsoever, for example, as a result of the machine being mobile andassuming a different inclination during operation.

For synchronization of the rotation motions of the rotary parts, in theillustrated example a synchronizing device of the gear wheelsynchronization type is provided. In this example, the synchronizingdevice 30 comprises, more precisely, two intermeshing gear wheels 31,32, in which the one gear wheel 31 is fitted to the cylinder drum 23 forrotation together with the latter about its rotation axis 22, whilst thesecond gear wheel 32 is fixedly attached to the drive shaft 20, next tothe driving pulley 29, for rotation together with the latter. All theserotary parts have surfaces which are facing toward or are located in aclosed chamber 33, which is enclosed by the machine housing 34. Thischamber 33 is intended to be wholly or partially filled with fluid, suchas hydraulic fluid, which can be the same hydraulic fluid as included inthe hydraulic system to which the machine belongs, either as a pump oras a motor. The oil or fluid in the chamber 33 is required for, in thefirst place, reducing the friction in contact surfaces between themoving parts, for cooling, for damping sound and for protecting againstcorrosion.

As a result of the moving parts executing a motion, essentially arotation motion, the fluid is jointly transported by the moving parts.In order to reduce the resultant energy losses, in this embodiment, too,a screening member in the form of a screen wall 35 is provided, which isshown in section in FIG. 2, whilst its basic shape can best be seen fromthe perspective view in FIG. 3. In this embodiment, too, the screeningmember 35 divides the fluid chamber 33 delimited by the housing 34 intotwo part-chambers, on the one hand a radially outer part-chamber 36,relative to the rotation axes 21, 22, and, on the other hand, a radiallyinner part-chamber 37. Like the previous embodiment, the radially innerpart-chamber 37 encloses the moving parts, which thus comprise thecylinder drum 23, with gear wheel 31 and axial pistons 24, and thedriving pulley 29 with associated gear wheel 32. The screen wall 35 hasa contour which, in this embodiment, over its longer portion, bends offboth inward and outward so as to adjoin relatively closely to the movingparts without coming into contact therewith and, in this embodiment,also has a highly smooth inside or inner surface 38, i.e. a low-frictionsurface so as to allow the fluid to slide around along the surface withleast possible friction, thereby maintaining a high Reynold's number forthe flow within the device, in combination with good flowcharacteristics. Examples of smoothness are steel which has been lathedbetter than normal, for example steel plating. The screen wall is notintended to separate the two part-chambers in a seal-tight manner,however, but rather to allow a small exchange of fluid between thechambers in order to exploit the larger total volume and hence maintainthe good properties of the fluid. All the same, care is taken to ensurethat the fluid in the outer part-chamber 36 is kept relatively still, sothat this fluid volume does not create any energy losses in the machine.The screen wall 35 follows roughly to a certain extent, though with aninterspace or a gap 41, the outer contour of the moving parts. Thescreen wall is chosen with as little radial distance as possible to therotation axes 21, 22 and, in other words, with the smallest possiblelever arm and circumference, whilst, at the same time, the annular gapwidth, i.e. the distance of the screen wall from the rotating parts,must be sufficient to provide room for the boundary layer which ispresent due to adhesion conditions. In a typical example of theillustrated type of pump/motor, the gap width 41 can lie within therange 10-20% of the diameter of the generatrix of the rotating partsover the majority of the axial length of the wall. This range is validfor this example, given normal hydraulic fluid viscosity and a certainorder of magnitude for the rotation speeds of a few thousand revolutionsper minute. At the edges of the wall and at places where there areirregularities of shape, major deviations occur in gap width, forexample in order to acquire rounded forms.

From the perspective view in FIG. 3 can thus be seen the basic shape ofthe screen member 35, which most simply resembles an angled pipe or apipe bend of circular cross section and two circular peripheral edges39, 40, facing away from each other, of which the one peripheral edgeextends in a radial plane relative to the one rotation axis 21, whilstthe other peripheral edge 40, i.e. its opening plane, extendssubstantially in a radial plane relative to the other rotation axis 22,though a certain angling may be expedient in practice.

The partially broken view according to FIG. 6 is intended to showprincipally the volume of the inner part-chamber 37. As a result of thesuccessive changing by the pistons of their axial position, over therevolution, in associated cylinder bores 25, the fluid volume will varyperiodically over the revolution also on the rear side of the piston,i.e. that which forms part of the volume in the inner part-chamber 37.When the pistons slide into the bore, a larger fluid volume is thusrequired on this part of the revolution compared with that part of therevolution in which the pistons slide in to a lesser degree. On theother hand, the interspace between the driving pulley 29 and thecylinder drum 23 has a greater volume on that part of the revolution inwhich the pistons jut out most. Through optimal configuration of thescreen wall 35, a complete equalization of these volume variations canalmost be achieved, which otherwise create pulsating pressure variationsover the revolution and thus are largely thereby equalized by means ofthe screen wall according to the invention. This is achieved, moreprecisely, by the area in an axial section through the innerpart-chamber 37 being kept substantially constant throughout therevolution and is thus accomplished by choice of the extent of thescreen wall, thereby reducing or eliminating a further source of energylosses. On the opposite side of the pistons 24 is found the hydraulicfluid, which either drives the pistons (motor) or is driven by thepistons (pump), but which, for the sake of clarity, is not marked inFIG. 6.

The invention is not limited to the examples which have been describedabove and illustrated in the drawings. It is conceivable, for example,for the outer part-chamber to have zero fluid volume, i.e. to be totallyfull, for example, or for the screen wall to be fully sealed againstthis part-chamber.

The inside of the housing can alternatively be configured and positionedsuch that the housing forms the smooth wall surface. Other variants ofrotating hydraulic pumps or motors in which the invention can directlybe applied are, for example, the “in-line” machine, which differs fromthe “bent axis” type in that the shaft of the cylinder drum and thedrive shaft are coaxial, but in that its swash plate is instead angledto the drive shaft. The invention does not only function in afixed-installation machine, for example having a horizontal rotationaxis, but works regardless of axis inclinations, for example in a mobileinstallation.

While the present invention has been described with reference to a fewspecific embodiments, the description is illustrative, of the inventionad is not to be construed as limiting the invention. Variousmodifications may occur to those skilled in the art without departingfrom the true spirit and scope of the invention as defined by theappended claims.

1. A device for reducing energy losses in a machinery unit (1), having at least one part (4, 6/23, 26, 29, 31, 32) which is arranged to rotate in fluid about a rotation axis (6/21, 22) in a substantially closed chamber (3/33) delimited in the radially outward direction by means of a wall (18/35) extending around said rotation axis, wherein said wall (18/35) has a radially inward facing wall surface (10/38) extending wholly or partially around said at least one part, said wall surface is a smooth low-friction surface against the fluid and extends close to, but with an interspace (41) to said at least one part, (4, 6/23, 26, 29, 31, 32), and wherein said interspace is suited to minimizing the rotating fluid volume and, at the same time, maintaining necessary width for a boundary layer formed in the fluid between said at least one part and said wall surface.
 2. A device for reducing energy losses in a machinery unit (1), comprising at least one part (4, 6/23, 26, 29, 31, 32) which is arranged to rotate in fluid about a rotation axis (6/21, 22) in a substantially closed chamber (3/33), wherein a screening member (8/35), which extends in the form of a screen wall wholly or partially around said at least one rotary part and is arranged to divide said chamber into an inner part-chamber (14/37) and an outer part-chamber (13/36), the screen member having opposite open ends through which fluid may pass and including a low-friction inner surface the fluid in said inner part-chamber rotating with said at least one part in its rotation motion, and in said outer part-chamber (13/36), said fluid substantially is not jointly transported upon rotation of said at least one part.
 3. A device for reducing energy losses in a machinery unit (1), having at least one part which is arranged to rotate in a fluid about a rotation axis (6/21, 22) in a substantially closed chamber (3/33) which is asymmetrical about said rotation axis, such that the volume of the chamber varies in the course of a rotation revolution, wherein by a screening member (18/35), which extends in the form of a screen wall around the rotary part and is arranged to divide the fluid chamber into an inner part-chamber (14/37) and an outer part-chamber (13/36), said inner part-chamber is delimited by a smooth screen surface of said screen wall and in which said fluid is allowed to rotate with said rotary part in its rotation motion, said screen wall further including opposite open ends each of which is defined by a circular peripheral edge, in said outer part-chamber said fluid is not jointly transported upon rotation of said rotary part, and said screen wall being situated such that the inner part-chamber is arranged to hold a fluid volume which is substantially invariable over said rotation revolution.
 4. The device for reducing energy losses in a machinery unit of claim 3, further comprising; a hydraulic rotating axial-piston machine including a drive shaft (20); and a driving pulley (29) which is angled relative to longitudinal axes of the axial pistons (24) for cooperation with the axial pistons, which axial pistons are movable to and fro in their cylinder bores (25) in said rotary part, wherein said rotary part is a cylinder drum (23) rotatable about said rotation axis (22).
 5. The device for reducing energy losses in a machinery unit of claim 4, wherein said drive shaft (20) and said rotation axis (22) of said cylinder drum (23) are angled relative to each other.
 6. The device for reducing energy losses in a machinery unit of claim 4, wherein said screening member (35) is configured as an angled pipe having two circular open ends radially spaced from respective axes, one of the axes being said rotation axis, said axes of said circular open ends being angled relative to each other.
 7. The device for reducing energy losses in a machinery unit of claim 6, wherein said screening member (35) is generally wedge shaped.
 8. The device for reducing energy losses in a machinery unit of claim 6, wherein an edge defining one of the two circular open ends extends in a radial plane relative to said rotational axis.
 9. The device for reducing energy losses in a machinery unit of claim 8, wherein said edge is a first edge and wherein a second edge defining the other of the two circular open ends extends in a radial plane relative to a rotational axis of said drive shaft.
 10. The device for reducing energy losses in a machinery unit of claim 3, wherein each of said circular peripheral edge having a diameter that is at least as large as a diameter of said smooth screen surface. 